What role does the diaphragm play in breathing?

The diaphragm is a crucial muscle in the respiratory system that plays a significant role in the process of breathing. When the diaphragm contracts, it moves downward, increasing the volume of the thoracic cavity. This expansion lowers the internal air pressure in the lungs compared to the outside atmosphere, which allows air to flow in—a process known as inhalation. Conversely, when the diaphragm relaxes, it moves back up, reducing the volume of the thoracic cavity and increasing the pressure in the lungs, which aids in expelling air during exhalation.

This cyclical process of expansion and contraction directly facilitates breathing by allowing for the intake of fresh oxygen and the expulsion of carbon dioxide, making the diaphragm essential for efficient respiratory function. Other choices, while they may touch on elements of the breathing process, do not accurately represent the main function of the diaphragm in its role as a muscle that enables the rhythmic motions required for breathing.